皮秒脉冲激光辐照时半导体的能量转换特性

CHARACTERISTICS OF ENERGY TRANSFER OF SEMICONDUCTOR DURING PICOSECOND LASER IRRADIATION

在皮秒脉冲激光辐照时，半导体材料表面的能量转换过程中，重点讨论能量从电子-空穴等离子体到晶格的转换过程。指出能量转换特性的最重要的弛豫过程是电子-声子相互作用，决定了由电子载流子系统到晶格的能量转换。实验表明电子和声子的能量交换时间小于10ps。硅表面反射率与Nd：YAG锁模激光器能量密度的关系曲线表明，当能量密度在0．5～0．83J／cm2之间，硅表面反射率为最大值，并且在低能量密度时，反射率的上升与材料相变到液态的程度在定量上是一致的。

The processes of energy transfer of semiconductor surface irradiated by picosecond laser pulses are studied. Discussion is focussed on energy transfer from the electron-hole plasma to the lattice.It is presented that one of the most important energy relaxation processes is the electron-phonon interaction,which determines the energy transfer from electronic carrier system to the lattice. The experiments indicate that the time of electron-phonon energy exchange is less than 10 ps. The curve of relation between the reflectivity of Si surface and the fluence densities of a mode-locked Nd:YAG laser shows that the reflectivity of Si surface passes through a maximum between 0. 5 and 0. 83 J/cm2 and the initial rise at low fluence densities is in quantitative agreement with a phase transition to the liquid state.